feat: add Sleeper based on futures-timer

backon/Cargo.toml

@@ -20,20 +20,23 @@ targets = [
 ]
 
 [features]
-default = ["std", "std-blocking-sleep", "tokio-sleep", "gloo-timers-sleep"]
+default = ["std", "std-blocking-sleep", "tokio-sleep", "gloo-timers-sleep", "futures-timer-sleep"]
 std = ["fastrand/std"]
 std-blocking-sleep = []
 gloo-timers-sleep = ["gloo-timers/futures"]
 tokio-sleep = ["tokio/time"]
+futures-timer-sleep = ["futures-timer"]
 
 [dependencies]
 fastrand = { version = "2", default-features = false }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 tokio = { version = "1", optional = true }
+futures-timer = { version = "3.0.3", optional = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 gloo-timers = { version = "0.3", optional = true }
+futures-timer = { version = "3.0.3", optional = true, features = ["gloo-timers"]}
 
 [dev-dependencies]
 anyhow = "1"

backon/src/lib.rs

@@ -41,11 +41,12 @@
 //! environments, they are gated under their own features, which are enabled
 //! by default:
 //!
-//! |      `Sleeper`      | feature            | Environment |  Asynchronous |
-//! |---------------------|--------------------|-------------|---------------|
-//! | [`TokioSleeper`]    | tokio-sleep        | non-wasm32  |  Yes          |
-//! | [`GlooTimersSleep`] | gloo-timers-sleep  |   wasm32    |  Yes          |
-//! | [`StdSleeper`]      | std-blocking-sleep |    std      |  No           |
+//! |      `Sleeper`       | feature            | Environment |  Asynchronous |
+//! |----------------------|--------------------|-------------|---------------|
+//! | [`TokioSleeper`]     | tokio-sleep        | non-wasm32  |  Yes          |
+//! | [`GlooTimersSleep`]  | gloo-timers-sleep  |   wasm32    |  Yes          |
+//! | [`FutureTimerSleep`] | future-timer-sleep |   both      |  Yes          |
+//! | [`StdSleeper`]       | std-blocking-sleep |    std      |  No           |
 //!
 //! ## Custom Sleeper
 //!

backon/src/sleep.rs

@@ -36,7 +36,11 @@ impl<F: Fn(Duration) -> Fut + 'static, Fut: Future<Output = ()>> Sleeper for F {
 /// The default implementation of `Sleeper` when no features are enabled.
 ///
 /// It will fail to compile if a containing [`Retry`][crate::Retry] is `.await`ed without calling [`Retry::sleep`][crate::Retry::sleep] to provide a valid sleeper.
-#[cfg(all(not(feature = "tokio-sleep"), not(feature = "gloo-timers-sleep"),))]
+#[cfg(all(
+    not(feature = "tokio-sleep"),
+    not(feature = "gloo-timers-sleep"),
+    not(feature = "futures-timer-sleep")
+))]
 pub type DefaultSleeper = PleaseEnableAFeatureOrProvideACustomSleeper;
 /// The default implementation of `Sleeper` while feature `tokio-sleep` enabled.
 ///
@@ -48,6 +52,15 @@ pub type DefaultSleeper = TokioSleeper;
 /// It uses `gloo_timers::sleep::sleep`.
 #[cfg(all(target_arch = "wasm32", feature = "gloo-timers-sleep"))]
 pub type DefaultSleeper = GlooTimersSleep;
+/// The default implementation of `Sleeper` while only the feature `futures-timer-sleep` is enabled.
+///
+/// It uses `futures_timer::Delay`.
+#[cfg(all(
+    not(feature = "tokio-sleep"),
+    not(feature = "gloo-timers-sleep"),
+    feature = "futures-timer-sleep"
+))]
+pub type DefaultSleeper = FuturesTimerSleep;
 
 /// A placeholder type that does not implement [`Sleeper`] and will therefore fail to compile if used as one.
 ///
@@ -78,6 +91,24 @@ impl Sleeper for TokioSleeper {
     }
 }
 
+/// The implementation of `Sleeper` that uses `futures_timer::Delay`.
+///
+/// This implementation is based on
+/// the [`futures-timer`](https://docs.rs/futures-timer/latest/futures_timer/) crate.
+/// It is async runtime agnostic and will also work in WASM environments.
+#[cfg(feature = "futures-timer-sleep")]
+#[derive(Clone, Copy, Debug, Default)]
+pub struct FuturesTimerSleep;
+
+#[cfg(feature = "futures-timer-sleep")]
+impl Sleeper for FuturesTimerSleep {
+    type Sleep = futures_timer::Delay;
+
+    fn sleep(&self, dur: Duration) -> Self::Sleep {
+        futures_timer::Delay::new(dur)
+    }
+}
+
 /// The default implementation of `Sleeper` utilizes `gloo_timers::future::sleep`.
 #[cfg(all(target_arch = "wasm32", feature = "gloo-timers-sleep"))]
 #[derive(Clone, Copy, Debug, Default)]